1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a sputter for deposition of a metal layer for a liquid crystal display device, and a method of fabricating a liquid crystal display device using a sputter.
2. Discussion of the Background Art
Cathode ray tubes (CRTs) have been widely used for display devices such as televisions and monitors. However, the CRTs have several disadvantages, for example, they are heavy, they occupy a large volume, and they require a high driving voltage. Accordingly, flat panel display (FPD) devices such as thin-film transistor-liquid crystal displays (TFT-LCDs) are being developed, which have high resolution, small depth and high color reproducibility. Moreover, the TFT-LCDs have become larger.
FIG. 1 is a schematic perspective view of a liquid crystal display device according to the background art.
In FIG. 1, a liquid crystal display (LCD) device 11 has an upper substrate 5 and a lower substrate 22, which face one another, and which are spaced apart from each other. A liquid crystal layer 14 is interposed between the upper substrate 5 and the lower substrate 22. The upper substrate 5, which is commonly referred to as a color filter substrate, includes a black matrix 6, a color filter layer 7, and a transparent common electrode 18 subsequently disposed on an inner surface thereof. The black matrix 6 includes openings having one of three sub-color filters 7a, 7b and 7c of red (R), blue (B), and green (G), respectively.
A gate line 13 and a data line 15 are formed on an inner surface of the lower substrate 22, which is commonly referred to as an array substrate, such that the gate line 13 and the date line 15 cross each other to define a pixel region “P.” A thin film transistor (TFT) “T” is formed at the intersection of the gate line 13 and the data line 15. A pixel electrode 17 is formed in the pixel region “P” to correspond to each of the sub-color filters 7a, 7b, and 7c, and is electrically connected to the TFT “T.” The upper substrate 5, the lower substrate 22, and the liquid crystal layer 14 interposed therebetween are together referred to as a liquid crystal cell.
FIG. 2 is a schematic cross-sectional view of a liquid crystal display device according to the background art.
In FIG. 2, a first substrate 22 and a second substrate 5 face each other and are spaced apart from each other. A gate electrode 32 of a conductive material such as metal is formed on an inner surface of the first substrate 22. A gate insulating layer 34 of silicon nitride (SiNx) or silicon dioxide (SiO2) is formed on the gate electrode 32. An active layer 36 of amorphous silicon is formed on the gate insulating layer 34 over the gate electrode 32, and an ohmic contact layer 38 of impurity-doped amorphous silicon is formed on the active layer 36. Source and drain electrodes 42 and 44 of a conductive material such as metal are formed on the ohmic contact layer 38 to constitute a thin film transistor (TFT) “T” with the gate electrode 32. A passivation layer 46 of an inorganic insulating material or an organic insulating material is formed on the source and drain electrodes 42 and 44. The passivation layer 46 has a drain contact hole 46a exposing the drain electrode 44. A pixel electrode 17 of a transparent conductive material is formed on the passivation layer 46 in a pixel region. The pixel electrode 17 is connected to the drain electrode 44 through the drain contact hole 46a. 
A black matrix 6 is formed on an inner surface of the second substrate 5. The black matrix 6 covers a boundary of the pixel electrode 17 to prevent light leakage at an area outside of the pixel electrode 17. The black matrix 6 also corresponds to the area of the TFT “T” to shield incident light into a channel of the TFT “T,” thereby preventing generation of photocurrent. A color filter layer 7 including red and blue sub-color filters 7a and 7b is formed on the black matrix 6. Even though not shown in FIG. 2, red, green and blue sub-color filters are alternately repeated such that each sub-color filter corresponds to one pixel electrode 17. A common electrode 18 of a transparent conductive material is formed on the color filter layer 7. A liquid crystal layer 14 is formed between the pixel electrode 17 and the common electrode 18.
The gate electrode 32, the source and drain electrodes 42 and 44, the pixel electrode 17 and the black matrix 6 are usually made of a metallic material. In general, the metallic material is deposited in a sputter through a physical vapor deposition (PVD) method. For a black matrix of an LCD device, a fabricating process will be illustrated in detail.
In an LCD device, the sub-pixel regions of an upper substrate are divided by a black matrix as described above. The black matrix, which is sometimes referred to as a light shielding film, prevents mixing of the red, green and blue colors, and improves the contrast ratio. In addition, the black matrix prevents radiation of other sub-pixel regions by electrons, and minimizes reflection of incident light so that images having high resolution and high definition can be displayed. Moreover, the black matrix shields light from the backlight unit by the sub-pixel regions, thereby clarifying the color of each sub-pixel region.
The black matrix can be made of a conductive metallic material such as chromium (Cr) through a photolithographic process, or made of conductive graphite or organic polymeric resin having low reflectance. In the case of a conductive metallic material, even though accumulated electrons in the black matrix are easily eliminated, the black matrix has relatively high reflectance. Thus, an additional metal oxide may be formed on the metallic black matrix. For example, chromium (Cr) and chromium oxide (CrOx) may be used as the black matrix and the metal oxide, respectively. After Cr and CrOx films are formed on a substrate by sequentially depositing Cr and CrOx in a sputter, a photoresist (PR) film is formed on the Cr and CrOx films. After exposing and developing the PR film to form a PR pattern, the Cr and CrOx films are etched. A black matrix is completed by subsequent cleaning and removing of the PR pattern. Generally, nitric acid of about 4% including Ce(NH3)2(NO3)6 of about 10 weight % is, used as an etching solution for the etching process, and water of room temperature is used as a cleaning solution for the cleaning process.
FIG. 3 is a schematic view showing a structure of a sputter according to the background art.
A sputter is a deposition apparatus of a thin film using a sputtering phenomenon. In a chamber of the sputter, first ions such as argon ions (Ar+) are accelerated and collide with a target having a low voltage, whereby second ions of the target are detached and deposited onto a substrate. In FIG. 3, a sputter 100 includes a chamber 105. In the chamber 105, a substrate 110 is loaded on a susceptor 120. The susceptor 120 is formed on a platen 130 which is movable up and down to adjust a gap between the substrate 110 and a target 140 disposed over the substrate 110. A magnet 150 is formed outside the chamber 105 to increase plasma density by generating a magnetic field. A shield mask 160 having an open portion “H” is formed between the target 140 and the substrate 110. The shield mask 160 determines a deposition region of chromium (Cr) and chromium oxide (CrOx) onto the substrate 110.
FIG. 4 is a magnified schematic view, which is a portion “A” of FIG. 3, showing a shield mask according to the background art.
In FIG. 4, since a shield mask 160 has an open portion “H” (of FIG. 3) smaller than a substrate 110, the shield mask 160 overlaps an edge of the substrate 110 with an overlapping distance “d1 ”, and the edge of the substrate 110 is screened by the shield mask 160 in an overlapping portion “C.” Accordingly, chromium (Cr) and chromium oxide (CrOx) are not uniformly deposited onto the edge of the substrate 110, while they are uniformly deposited onto a central portion of the substrate 110 through the open portion “H.” Since Cr and CrOx films have non-uniform thickness in the overlapping portion “C,” the Cr and CrOx films of the overlapping portion “C” cannot be used for a black matrix. As an LCD device is enlarged, the demand for full utilization of a substrate increases. However, since an edge of a substrate cannot be used due to non-uniformity of thickness, utilization efficiency of the substrate is relatively low. These disadvantages not only affect the black matrix, but also affect the other metal layers formed by sputtering, such as the gate line including the gate electrode, the data line including source and drain electrodes, the pixel electrode, and the common electrode.